Electrical Grounding – Copper vs. Aluminum Ground Wire Comparison

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My house was built in the 70s and originally had all aluminum wiring. New circuits have been added over the years and the house currently has a mix of both aluminum circuits and copper circuits, along with a newer 200A panel. I have owned the house for about the past 5 years. There is currently a #2 aluminum stranded ground wire connecting the panel to my water line where the water line enters my basement. The panel and water line entrance are at opposite corners of the basement. That ground wire runs along the underside of my floor joists instead of passing through holes drilled in the joists. This wire is in the way of where some top plates will be going for walls that i am building to finish the basement, so i want to re-route the ground wire to a new path that is not in the way. The new path will be about 20 feet longer than the current run, so I am planning to buy new wire to make this new run from my panel to the water line. Should i replace the current #2 aluminum wire with a longer #2 aluminum wire, or can/should i go with a copper wire instead? The copper costs more but it is easier to work with and i think i would prefer changing to copper unless there is some reason to keep it aluminum.

Best Answer

I would recommend 4 AWG copper, which is equivalent (in general terms) to 2 AWG aluminum. Smaller, easier to run. More standard. And compatible with the copper pipe you're bonding it to.

But while you're doing that, check your local codes (might be worth a call to the building department or equivalent organization). While almost anything old can be grandfathered, once you are going to this trouble you might as well do whatever current local code requires. Which could be any combination of:

  • Copper water pipe
  • One ground rod with a test
  • One ground rod without a test (normally that's only when you also ground to the water pipe)
  • Two ground rods without a test
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